There are basically four known methods for obtaining crystal bodies having a desirable orientation.
(1) First, the simplest method is a method wherein a block-like single crystal is prepared and then a crystal body is cut out therefrom in a desired orientation in accordance with the measured result of single crystalline orientation.
In this method, however, the cutting takes a long time, the cost is high, and also the size of the single crystal to be prepared is critical. .Therefore, the mass production can not be expected.
(2) Second, there is a so-called strain-slant annealing method.
This method is a method of growing a single crystal of desirable orientation from an end of a sample, wherein a seed crystal is first prepared on the end of the sample and rotated in a desired direction to grow the whole of the seed crystal into a single crystal having the desirable orientation, and has been proposed by Fujiwara et al [T. Fujiwara and T. Hudita; J. Sci. Hiroshima Univ. A8 (1938), P293.about.296].
They have succeeded in the preparation of single crystals by the above method from aluminum and further from pure iron.
Thereafter, Dunn et al have applied the above method to silicon steel sheets having a large size [C. G. Dunn and G. C. Nonken: Metal Progress, 64 (1953) 6, P71.about.75].
According to their method for growing a plate crystal having a specified crystalline orientation, an end of a sample previously subjected to a strain is placed in a high temperature region of a temperature tilting furnace to prepare some seed crystals as shown in FIG. 1a, among which a crystal grain having an adequate orientation is selected and cut out as shown in FIG. 1b. Then, a necked portion of the cut out crystal grain is bent as shown in FIGS. 1c and 1d to align the seed crystal into a predetermined orientation with respect to the sample plate. Next, the seed crystal is annealed through heating in the temperature tilting furnace so as to grow over the whole of the plate, whereby the object is achieved.
In this method, however, it is necessary to strictly control the operation for selecting and cutting out a seed crystal having an adequate orientation from many crystal groups and the operation for bending the seed crystal into a predetermined orientation, which takes much labor and long time, so that the mass production can not be expected.
(3) Third, there is a method utilizing secondary recrystallization phenomenon.
The secondary recrystallization is a phenomenon that a seed of nucleating secondary grains largely grows through grain boundary energy of primary recrystallized grains as a driving force, which is widely utilized as a method of producing grain oriented silicon steel sheets as is well-known.
The grain oriented silicon steel sheet is required to have excellent magnetic properties in the rolling direction. That is, it is required that as the magnetizing force (magnetized properties), the magnetic flux density represented by B.sub.10 value (magnetic flux density in the rolling direction produced when the magnetizing force is 1000 A/m) is high and the iron loss represented by W.sub.17/50, value (iron loss when being magnetized at a magnetic flux density of 1.7 T and a frequency of 50 Hz) is low so that it is fundamentally necessary to highly align &lt;001&gt; axis of secondary recrystallized grains in steel into the rolling direction. For this end, fine precipitates such as MnS, MnSe and the like are generally added as an inhibitor, and further, if necessary, a small amount of Sb as disclosed in Japanese Patent Application Publication No. 51-13469, a small amount of Mo as disclosed in Japanese Patent Application Publication No. 57-14737 or a combination of Al, N, Sn, Cu and the like as disclosed in Japanese Patent Application Publication No. 60-48886 is added, which are properly combined with treating conditions in each of hot rolling and cold rolling, whereby high magnetic flux density and low iron loss grain oriented silicon steel sheets having a B.sub.10 value of magnetic flux density of more than 1.90 T and a W.sub.17/50 value of iron loss of not more than 1.05 W/kg (thickness 0.30 mm) have been produced recently.
Furthermore, a technique of producing bidirectional oriented silicon steel sheets by crossly conducting the cold rolling is proposed in Japanese Patent Application Publication No. 35-2657 and the like.
However, in order to highly align &lt;001&gt; axis of secondary recrystallized grains in the product into the rolling direction or a direction perpendicular to the rolling direction, it is necessary to adjust the components and strictly control complicated and many steps of steel-making, hot rolling, cold rolling and heat treatment. In the actually industrial production, however, the treating conditions are apt to be shifted from the totally proper conditions as mentioned above. If the treating conditions are slightly shifted, there is caused a problem that the orientation of &lt;001&gt; axis into the rolling direction or the direction perpendicular to the rolling direction becomes poor.
Lately, it has been attempted to thin the thickness of product plate to reduce the iron loss. However, as the final thickness becomes thin, the alignment of &lt;001&gt; axis of secondary recrystallized grains into the rolling direction or the direction perpendicular to the rolling direction becomes unstable, so that the improvement thereof is strongly demanded.
In Japanese Patent Application Publication No. 58-50295 is disclosed a method utilizing the same method as described in the item (2), wherein secondary grains locally subjected to secondary recrystallization are used as a seed and a temperature gradient is applied to a steel sheet at a boundary between primary and secondary recrystallization regions to grow the seed. However, the production as a commercial material is not yet attained at the present.
As a basic problem, the resulting crystalline orientation range is restricted in the aforementioned secondary recrystallization method, and consequently there is a problem that the orientation largely shifted from (110)[001] orientation or (100)[001] orientation is not obtained.
(4) Fourth, there is a method utilizing third order recrystallization.
The third order recrystallization proceeds through surface energy as a driving force, which is utilized for mainly growing (100)[hkl] grains in bidirectional oriented silicon steel sheet or the like, but there are problems on atmosphere control at high temperature, accuracy of orientation control and the like.
As mentioned above, the mass production can not be achieved in the method capable of strictly controlling to a specified orientation, while the orientation selectivity and control accuracy come into problem in the method capable of industrially conducting the mass production, so that methods capable of conducting the mass production and strictly controlling to the specified orientation are not yet known up to the present.
Moreover, the production of single crystals through solidification method wherein a seed crystal is planted on an end of molten liquid metal and gradually cooled below the melting point to grow the seed crystal into a large crystal is known as a Bridgeman method or a Tanmann-Bridgeman method from the old time. However, the invention is a technique that a treating material growing the seed material is not liquid but is a solid having a crystal structure, and is entirely different from the aforementioned solidification method.
As mentioned above, if it is intended to strictly control the crystal into the specified orientation, much labor and long time are taken for obtaining a proper seed, so that the mass production can not be conducted industrially. On the other hand, if it is intended to conduct the mass production, the seed is necessary to be prepared by rolling and recrystallization, so that there is caused a problem on the accuracy of controlling to the specified orientation due to the scattering of production conditions. Furthermore, the growing orientation is restricted from a viewpoint of the essential crystal structure of the starting material, so that there is remaining a problem that the orientation can not be selected.
In this connection, the inventors have already found a method of directly planting a previously and strictly controlled seed crystal on a steel sheet through welding as a method of preparing nucleus of secondary recrystallized grains without rolling and recrystallization in the production of grain oriented silicon steel sheets and disclosed in Japanese Patent laid open No. 63-149318.
In this method, however, the quality of joint portion is changed by the heat affection in the welding, so that there is remaining a problem that it is very difficult to preferentially grow the planted secondary grain nucleus stably over the weld portion.